As known by those skilled in the art, a number of factors determine the suitability of a process for forming a foamed product of the type in which a blowing agent forms cells in a synthetic resin as the resin is cured. Most significantly, the interaction of the rate of cure and the rate at which the blowing gas is generated must be such that the correct foam volume is attained. If the resin cures too rapidly there is inadequate time for the gas to form the proper size and number of gas voids in the finished product. Over expansion of the forming foam product must also be avoided. Rapid expansion due to a slow cure rate may cause the expanding foam to simply collapse as a result of inadequate wall strength surrounding the individual gas cells.
A number of prior art techniques are available to control the rate of foam expansion and the cure rate. For example, a wide range of reactivities are available in commercial resins and curing agents. In addition, resins are available in a range of viscosities which is another parameter which can be used to control foam expansion rate. That is, it is known that a low viscosity resin can generally be expanded to a greater volume with a given volume of gas than a higher viscosity material; however, the resin must have sufficient viscosity to contain the gas at the pressures at which it is generated in order for the foam to be properly formed.
Particularly in automotive applications, foamed products must have good environmental resistance and, most significantly, in many applications they must protect metal from corrosion. In the past many foamed parts were made using polyurethane which provides a number of desirable attributes. It is known, however, that alternatives to urethane-based foams are frequently more environmentally desirable, in part due to unreacted functional groups in the finished products and difficulty in handling isocyanate functional chemicals in manufacturing processes.
In U.S. Pat. No. 4,623,478 entitled, Composition and Method for Making Foamed Polyester Resin, foams from unsaturated polyester resin are described which employ carbonate and bicarbonate salts. More specifically, blowing agents are used which include a salt selected from sodium and potassium carbonates and bicarbonates and water intermixed with a free-flow agent to absorb the water and render the composition a free flowing powder. It is stated that these compositions are useful in methods of creating a foam structure in polyester resin products by providing a source of gas for expansion of the resin. It is further stated therein that over the years unsaturated polyesters have been foamed by generating CO.sub.2 gas through the acid decomposition of carbonate and bicarbonate salts by mixing the carbonate salt directly into the unsaturated resin mass with an acid. A system of curing agents for achieving cross-linking of the polyester resin is described.
In U.S. Pat. No. 4,119,583 entitled, Foamed Articles and Methods for Making Same, a rigid polyester foam is described which it is stated can be made without the application of heat or the use of emulsions of resin and water. It is stated that cells are blown in the resin by the reaction of inorganic acids with carbonates. Carbon dioxide is thereby liberated which forms gas voids in the resin as the resin is cured. A system of curing agents for achieving cross-linking of the polyester resin is described.
In U.S. Pat. No. 4,016,112 entitled, Process for the Production of Foamed Resin Structure, a method of producing a foamed article is described which is characterized by the synchronization of the generation of carbon dioxide by a reaction of acid esters of phosphoric acid and/or acid esters of phosphorous acid with metal carbonates and/or metal bicarbonates with respect to the polymerization with curing of a curable resin composition. The use of 1,2-polybutadiene polymers is described therein which, it is stated, can be modified and lists epoxide-modified materials, maleic-acid-modified materials and urethane-modified materials as examples thereof.
It is an object of the present invention to provide a method of forming a foamed synthetic resin which does not rely on polyurethane as the base resin.
It is a further object of the invention to provide a method of forming a foamed product which can be cured at room temperature without the addition of external heat.
It is a further object of the present invention to provide a method of forming a foamed product which uses epoxy as the base resin.
It is still a further object of the present invention to provide method of forming a foamed product which is a liquid-based system that can be utilized with equipment designed for liquid material dispensing.
It is still a further object of the present invention to provide a foamed product made in accordance with the method of the present invention.